This invention relates to vapor compression refrigeration systems used for refrigeration and/or air conditioning purposes, whether or not employed as part of heat pump systems.
State of the art refrigeration systems operating on the vapor compression cycle conventionally feed the evaporator with refrigerant that is in both the liquid phase and the vapor phase. In a typical system, the vapor phase refrigerant is about 30% of the total mass flow rate. Inasmuch as refrigerant vapor has a lower density than liquid refrigerant, a higher speed of the mixture is required when the mass flow rate is kept constant if the percentage of the mixture in the vapor phase is increased. This leads to a higher pressure drop inside the conduits in the evaporator than would be the case for a liquid or a two phase fluid where a lesser percentage of the total mass flow rate was in the vapor phase.
As is well known, high pressure drops are highly undesirable in systems operating on the vapor compression cycle. High pressure drops lead to heat exchange inefficiency,the requirement for oversized heat exchangers with flow paths of a larger total cross sectional area to minimize the pressure drop, increased compressed energy costs and the like.
To solve these difficulties, it has been proposed in, for example, U.S. Pat. No. 4,341,086 issued Jul. 27, 1982 to Ishii to employ a phase separator located downstream of an expansion device that in turn receives compressed refrigerant from the condenser or gas cooler of the system. The phase separator provides liquid refrigerant to the evaporator and provides for bypassing of the evaporator by the vapor phase. Consequently, the velocity of the refrigerant through the vapor is considerably reduced because only liquid phase refrigerant is entering it. In addition, there may be improved distribution of refrigerant on the inlet side of the evaporator leading to increased efficiency of the evaporator.
However, and as is also well known, it is conventional to employ a lubricant in the refrigerant to provide lubrication of the compressor during system operation. In the Ishii system, and those like it, the lubricant is frequently dissolved in the liquid refrigerant or of a density much more closely approaching the density of the liquid refrigerant than the refrigerant vapor and as a consequence is fed through the evaporator with the liquid refrigerant. The lubricant can adversely affect heat exchange within the evaporator and thus some of the advantages of phase separation taught by Ishii are lost.
U.S. Pat. No. 5,996,372 issued Dec. 7, 1999 to Koda et al. discloses the use of an accumulator intended for use in a refrigeration system and which provides a means for separating lubricant. However, the use of the accumulator at a particular location in a system to achieve maximum efficiency is not particularly well described. Moreover, the accumulator itself, with its provision for oil separation is unduly complicated and costly.
The present invention is directed to overcoming one or more of the above problems.
It is the principal object of the invention to provide a new and improved refrigeration system. More specifically, it is an object of the invention to provide such a system with a means for separating refrigerant into liquid and vapor phases before it is flowed to an evaporator along with provision for assuring that lubricant contained within the refrigerant is constantly circulated to prevent lack of lubrication of the compressor during operation.
An exemplary embodiment of the invention achieves the foregoing objects in a structure including a compressor having an inlet and an outlet. A heat exchanger is provided for receiving compressed, lubricant containing refrigerant from the compressor outlet and cooling the refrigerant. Also included is an evaporator for evaporating refrigerant and cooling another fluid and returning the refrigerant to the compressor inlet. A phase separator is interposed between the heat exchanger and the evaporator for receiving cool refrigerant from the heat exchanger. The phase separator includes a chamber having an inlet connected to the heat exchanger, an upper vapor outlet adapted to be connected to the compressor inlet for delivering a vapor stream thereto and a liquid refrigerant outlet at a first level in a lower part of the chamber and connected to the evaporator. The phase separator also includes a lubricant outlet at a second level in the lower part of the chamber which is different from the first level. A lubricant conduit is connected to the lubricant outlet and to the compressor inlet for delivering lubricant separated in the phase separator to the compressor to lubricate the same by discharging lubricant into the vapor stream. Also included is a bypass conduit connected to the vapor outlet and to the compressor inlet to deliver the vapor stream to the compressor.
In a highly preferred embodiment, the lubricant conduit terminates in an eductor located in one of the vapor outlet and the bypass conduit.
In an even more preferred embodiment, the lubricant conduit is a capillary conduit having one end located in the chamber and serving as the lubricant outlet and an opposite end located in the vapor outlet serving as the eductor.
In one embodiment, the lubricant outlet is located below the liquid refrigerant outlet.
In an even more preferred embodiment of the system, the same includes a suction line heat exchanger having first and second flow paths in heat exchange relation with one another. The first flow path connects the heat exchanger and the phase separator and the second flow path connects the bypass conduit and the evaporator to the compressor inlet.
Other objects and advantages will become apparent from the following specification taken in connection with the accompanying drawings.